Seismic isolation device and manufacturing method of the same

ABSTRACT

A composite metal core  30  incorporated in a laminated rubber bearing for damper having two different kinds of metal material. An outer metal  31  includes a material having a high rigidity and an excellent plastic deformability. An inner metal  32  includes a material having low rigidity and an excellent plastic deformability. By making a rising rate of a bending rigidity of the composite metal core higher than a rising rate of a shear rigidity of the composite core, the composite metal core enters a deformation mode in which a superior shear deformability is created. In that deformation mode, the performance of absorbing energy generated in a process of plastic deformation is stabilized. And at the same time, an average horizontal shear yield stress degree of the composite metal core can be set at an arbitral level between the horizontal shear yield stress degrees of the two kinds of metal.

This Application claims priority to Japanese Patent Application No.JPA2014-122757, filed 13 Jun. 2014, now Japanese Patent No. 5661964,issued 12 Dec. 2014, the complete disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a seismic isolation device capable ofsafely protecting a building from an earthquake, and especially alaminated rubber bearing equipped with a damper for absorbing energy.

BACKGROUND OF THE INVENTION

A seismically isolated structure can reduce a response vibration of abuilding itself caused by strong earthquake ground motions. Therefore,the seismically isolated structure can enhance a holistic seismic safetyof an entire building including a skeleton framework as a container andinteriors such as furniture and equipment.

In order to realize the seismic isolation of structures, a seismicisolation device needs to have an isolator function capable of largelydeforming in horizontal direction while supporting the weight of thebuilding and a damper function for absorbing vibration energy of thebuilding input by the earthquake. Some seismic isolation device systemshave been already used practically. For example, several types usinglaminated rubber bearings are in practical use, such as 1) a combinationsystem of laminated natural rubber bearings and hysteretic metal dampersseparately provided from the rubber bearings, 2) a type of a laminatedrubber bearings using a high damping rubber compound, and 3) a type of alaminated rubber bearing having a lead core, or the like. Further, 4) asliding bearing type of seismic isolation device and 5) a rollingbearing type utilizing roller ad ball bearings of seismic isolationdevice are also in practical use.

Among the above seismic isolation devices, 3) so-called LRB (Lead RubberBearing), the laminated rubber bearing with lead core, which wasinvented and developed in New Zealand, has been highly evaluated in theworld and applied to a lot of actual isolated structures (see PatentDocuments 1 and 2). This device incorporates a lead core, which servesas a damper (an energy absorbing mechanism), at a center place orseveral places of the laminated rubber bearing as an isolator, in theplane view. This is one of the highly-evaluated seismic isolationdevices in the world including Japan and other countries (including NewZealand, the United Stated, Italy, Taiwan, Turkey, China, and SouthAmerica).

This seismic isolation devise is provided with both the isolatorfunction and the damper function in one device. By changing a rationbetween the lead core having the damper function and the laminatedrubber bearing having the isolator function, it becomes possible torather freely control the seismic isolation performance i.e., arestoring force of the device.

However, a wave of a social recognition for an environmental problem inrecent years causes a trend against a toxic potential of lead.Accordingly, it is suggested to employ a superplastic metal having asuperior plastic deformation property like lead as a material of thecore. Specifically, “a laminated rubber bearing having a tin core (leadplug) (Patent Document 3)” employing tin having a face-centered cubiclattice of crystalline structure same as lead, or tin-bismuth alloy, ora laminated rubber bearing employing zinc-aluminum alloy (PatentDocument 4) are suggested.

Other than above, the following materials are suggested as corematerials for absorbing energy; a polymer material such as a rubberhaving a high damping property, a mixed molding of two plastic resinmaterials each having different rigidities (Patent Documents 5 and 6);and an artificial damper material formed by molding a mixture of apolymer material such as a rubber and a granulated material such as ironpowder or glass beads (Patent Document 7).

PRIOR ART DOCUMENTS

(Patent Document 1) Japanese patent application publication No.SH059-62742;

(Patent Document 2) Japanese patent No. 3024562;

(Patent Document 3) Japanese patent application publication No.2008-082386;

(Patent Document 4 Japanese patent application publication No.2007-139108;

(Patent Document 5) Japanese patent application publication No.2005-009558;

(Patent Document 6) Japanese patent application publication No.2007-092818; and

(Patent Document 7) Japanese patent application publication No.HEI9-177368.

SUMMARY OF THE INVENTION Problem to be Resolved by the Invention

FIG. 1 shows a basic configuration of a conventional seismic isolationdevice incorporating a damper (metal core). FIG. 1 (1) is a verticalsectional view of the conventional seismic isolation device. FIG. 1(2)is a horizontal sectional view of the conventional seismic isolationdevice. A laminated rubber bearing body 1 incorporates a metal core 3 atits center part. Thick steel plates 25 are disposed near the upper andlower ends of the laminated rubber bearing body 1. Flanged steel plates4 are disposed outside of the thick steel plates 25 in the upper-lowerdirection. In this example, the metal core 3 has a circular plane shapein the plane view, and the metal core 3 is disposed at center part ofthe laminated rubber bearing body 1 in the planer view and surrounded bythe laminated rubber bearing body 1.

A metal core incorporating type of seismic isolation device, forexample, incorporating a lead-cored laminated rubber bearing called“LRB” or a tin-cored laminated rubber bearing called “SnRB”, and aseismic isolation device incorporating a core comprising artificiallymixture of rubber and iron powder have the following configurations.

As shown in FIG. 1, the laminated rubber bearing body 1 has elasticmaterials 11 (generally, laminated rubber bearing) and rigid materials 2(generally, steel plate), each having a plate shape and alternatelylaminated in the vertical direction. At least one core 3 for absorbingenergy with its plastic deformation is disposed inside the laminatedrubber bearing body 1. Normally, one core 3 for absorbing energy isdisposed at the center part of the laminated rubber bearing body 1 inthe plane view, although a plurality of cores 3 can be dispersedlyarranged when employed in a large seismic isolation device in which theplane size of the laminated body is particularly large.

By increasing the size of the core having a function for absorbingenergy, the damping performance of the seismic isolation device can beenhanced. However, if a ration of the diameter (plane size) of the coreto that of the laminated rubber bearing body becomes greater than apredetermined ratio, a horizontal deformation mode of the laminatedrubber bearing body can be broken, or a stability of the laminatedrubber bearing body and a vertical load support capacity will be unsurewhen the laminated rubber bearing body is deformed horizontally.Accordingly, normally, the diameter of the core is limited to about 20%or less of the diameter of the laminated rubber bearing body.

The damping performance can be also controlled by choice of the corematerial. Therefore, as described in the above Patent Documents, variousmaterials are suggested as the damper (core) material incorporated inthe laminated rubber bearing body. However, the resistance force of thecore comprising the resin material or the granular material (in examplesof Patent Documents 5 to 7) is low (the shear resistance force (stresslevel) per unit sectional area is low).

Hence, if the resin material or the granular material is employed in theseismic isolation devise for a large and heavy building, a core havingextremely large diameter is required, this being not realistic,although. Therefore, the resin material or the granular material can beemployed in only a house having a small size and a light weight such asa single-family house or the like.

Accordingly, considering the resistance force (stress level) of thematerial, metals are suitable to the damper (core) of the seismicisolation device for the large and heavy building, after all.

In Patent Document 3, alloy materials, such as tin-bismuth alloy, andtin-indium alloy are suggested as the core material. However, thosematerials are melted at extremely low melting points (between 117 and138° C.), as shown in Table 1

TABLE 1 composition and mechanical properties of alloy materials havinglow melting points (quotation from Patent Document 3) Compositionmelting breaking stretch (% by weight) point strength rate Sn Bi In Zn(° C.) (Mpa) (%) Sn—Zn alloy 92 0 0 8 199 71.0 55.2 Sn—Bi alloy 42~4358~57 0 0 138 55.1 200.0 Sr—In alloy 48 0 52 0 117 18.0 37.2

The core of the seismic isolation devise absorbs the earthquake energyby plastically deforming along with the shift of the plurality ofisolator layers with one another. Therefore, at the time of theearthquake, the core generates heat due to the absorbed energy. Numerousexperiments shows that the temperature increase of the core easilyexceeds 100° C. when a great earthquake vibration occurs.

Accordingly, when exposed to a great earthquake vibration, the abovealloy materials having the low melting points have a high possibility tobe molted. Further, even before the alloy materials are melted, theresistance force of the alloy materials has declined due to the hightemperature. As the result, the energy absorbing performance of thealloy materials drops greatly. Hence, these alloy materials having thelow melting point, although being plastically deformable metals, areunsuitable as core materials for absorbing the energy at the time of agreat earthquake.

Lead, tin, aluminum, zinc, copper, and an alloy of them are drawingattention as metal materials having superior plastic deformationperformances. Table 2 shows basic (mechanical) properties (longitudinalelastic modulus E, shear elastic modulus G, volume elastic modulus K,Poisson's ratio v, melting point, density at room temperature and atmelting point or the like) of these representative superplastic metalmaterials.

TABLE 2 mechanical properties of representative superplastic metalmaterials Sign unit lead tin aluminum zinc copper crystal structure facetetragonal face hexagonal face centered crystal centered crystalcentered cube cube cube longitudinal E Gpa 16.0 49.9 70.0 108.0 110-28elastic modulus shear elastic modulus G GPa 5.6 18.0 26.0 43.0 48.0volume elastic modulus K GPa 46.0 58.0 76.0 70.0 140.0 poisson's ratio υ— 0.44 0.36 0.35 0.25 0.34 melting point θ m ° C. 327.50 231.97 660.32419.53 1084.62 liquid density at melting point ρ m g/cm³ 10.66 6.99 2.386.57 8.02 density at room temperature ρ r g/cm³ 11.34 7.37 2.70 7.148.94 (β) average density between ρ ave g/cm³ 11.00 6.99 2.54 6.86 8.48room temperature and melting point

As is well known, among the above metal materials, the most widelyemployed as the core of the seismic isolator device is pure lead havingpurity of 99.99% or more. Lead is a superplastic metal having amechanical property capable of greatly plastically deforming. However,as lead has toxicity to human body, there is a tendency to hesitate touse lead material, amid the trend of rising environmental healthawareness. Further, the resistance force of lead is slightly low as thedamper material. Therefore, improvement is desired.

On the other hand, tin draws attention as a nontoxic superplastic metalinstead of lead having toxicity. Tin-cored ruminated rubber is put intopractical use and steadily achieves results. However, the resistanceforce of tin is about two times of lead. Therefore, the resistance forceof tin is slightly high when tin core is incorporated in the laminatedrubber bearing.

Further, the resistance force of tin is linked its rigidity. Therefore,the resistance force of tin becomes high along with its deformationunlike lead capable of deforming with a constant resistance force in itsplastic deformation region. This means that tin is inferior to lead inthe plastic deformability.

Table 3 shows a comparison between lead and tin in thermal propertiesand in mechanical properties. In terms of the thermal properties, tinhas a fatal drawback. That is, the melting point of tin is lower thanlead by around 100° C., while the resistance force (shear yield stressintensity) of tin is about two times higher than that of lead.

TABLE 3 comparison between lead and tin in thermal properties andmechanical properties sign unit lead tin aluminium zinc copper atomicweight g/mol 207.2 118.71 26.98 65.38 63.55 melting point θ m ° C.327.50 231.97 660.32 419.53 1084.62 {circle around (1)} ρ ave g/cm³327.50 175.34 343.65 242.46 574.09 heat capacity (at 25° C.) Ho J/(molK)26.65 27.11 24.20 25.47 24.44 specific heat J/(gK) 0.129 0.228 0.8970.390 0.385 criterial core data criterial core dimension 200 mm φ × H400mm core weight Wo kg 138.23 87.84 31.89 86.14 106.56 shear yield stressintensity τ (N/mm²) 8.0 14.8 horizontal resistance force Qd kN 251.33464.96 ±30 cm × 1 cycle E_(d30) kNm 301.6 557.9 deformation E {circlearound (2)} Hm KJ 5467.1 4252.4 18314.2 13407.6 43630.2 {circle around(3)} Ncm — 18.1 7.6 {circle around (1)}average density between roomtemperature and melting point {circle around (2)}heat amount for meltingcriterial core {circle around (3)}cycle number of vibration appliedbefore criterial core is melted

Now, it is assumed that a laminated rubber bearing (diameter: 1000 mmφ),incorporating a core (diameter: 200 mmφ, height: 400 mm), which is themost standard (general) type of laminated rubber bearing used in abuilding, horizontally deforms ±300 mm due to a great earthquake. Inthis assumption, the cycle number of vibration applied to the metal coreis calculated, starting at 20° C., which is an assumed temperature ofplug before the earthquake occurs, up until at the melting point of themetal core. As shown in the lower half of Table 3, the cycle number oflead core is around 18 cycles, while the cycle number of tin core is 7.6cycles, i.e. tin core reaches its melting point at one-thirds of cyclenumber of lead.

This difference is caused by the difference of the resistance forcebetween lead and tin. That is, since the resistance force of tin isabout two times of lead, the amount of absorbing energy per a cycle(calorific value) also becomes about two times of lead. Further, thisdifference is caused by the difference of the melting point between leadand tin. That is, the melting point of tin is lower than lead by at most100° C.

Note that since the resistance force of tin becomes lower along withtemperature rise caused by the energy absorption, the actual cyclenumber at which the temperature of tin core reaches its melting pointbecomes somewhat greater than the above cycle number. Anyway, it isclear that the energy absorption performance of tin is sharplydeteriorated at an early stage due to the lowered resistance force.

Especially, assuming the case of a great earthquake of magnitude 9level, which is likely to occur at Nankai Trough nearer to the mainlandthan Great East Japan earthquake in 2011, the metal core is likely to besubject to repeated vibrations with amplitude larger than expected, overa long period of time. Hence, tin-cored ruminated rubber has seriousproblems against the above earthquake.

The above arguments and questions on the core for the seismic isolationdevice (laminated rubber bearing) are summarized below.

Since the resistance force of the core comprising the polymer materialis low, the damper function is also low. Further, even if a larger sizedcore comprising the polymer material is used to raise the resistanceforce, the devise itself becomes unstable in turn. Therefore, thepolymer material is unsuitable as the core material for the seismicisolation device.

Further, the alloy materials having the low melting points (Table 1)easily reaches the melting points when absorbing energy. Therefore, thealloy material is similarly unsuitable as the core material for theseismic isolation device.

After all, lead and tin, which have made a lot of achievements, areviable options as the core material for the seismic isolation device.However, as shown in tables 2 and 3, it can be seen that there is widedifferences in the elastic modules and the shear yield intensity betweenlead that is most flexible material and tin that is the second flexiblematerial. Specifically, tin has more than three times of elastic modulesand about two times of shear yield intensity compared with lead,although the other materials have greater difference in the elasticmodules and the shear yield intensity from lead and tin.

In short, lead is rather flexible as the core material for the seismicisolation device, although having an excellent deformation property. Onthe other hands, since tin is too rigid, tin is also inferior to lead indeformation property. Other materials such as aluminum, zinc, and copperare more rigid than tin. Furthermore, lead has a problem of toxicity.

As described above, the demand of the rigidity forces the use of themetal material as the core for the seismic isolation device. However,when the some conditions (i.e. rigidity, deformation property,mechanical properties, environmental health, and safety handling(non-toxicity)) are considered, an idealistic metal core material,meeting all of the above conditions, does not exist.

Means of Solving of the Problems

The present invention employs following configurations to solve theproblem discussed above.

Configuration 1

A seismic isolation device includes: a laminated rubber bearing bodyformed by alternately laminating a plurality of elastic materials and aplurality of rigid materials in a vertical direction, each elasticmaterial and each rigid material having a thin plate shape; and acomposite metal core disposed inside the laminated rubber bearing bodyand plastically deformable to absorb energy. The composite metal coreincludes an inner metal and an outer metal. The outer metalconcentrically surrounds the inner metal in a horizontal cross-sectionalview. The inner metal and the outer metal are disposed in closeadherence with each other. The outer metal has an elastic modulus and anyield rigidity greater than the inner metal so that a sheardeformability of the composite metal core becomes greater than a bendingdeformability of the composite metal core.

A horizontal shear resistance force QC of the composite metal core in apredetermined cross-sectional area is set to satisfy an equation:QB≦QC<QA, the QA being a horizontal shear resistance force in thepredetermined cross-sectional area of a metal core A comprising thesingle outer metal, the QB being a horizontal shear resistance force inthe predetermined cross-sectional area of a metal core B comprising thesingle inner metal.

Configuration 2

In the seismic isolation devise according to configuration 1, any one ofCombinations 1 to 4 (Combination 1: tin for the outer metal and lead forthe inner metal, Combination 2: aluminum for the outer metal and lead ortin for the inner metal, Combination 3: zinc for the outer metal and anyone of lead, tin and aluminum for the inner metal, Combination 4: copperfor the outer metal and any one of lead, tin, aluminum and zinc for theinner metal) is employed as a combination of a material composing theouter metal and a material composing the inner metal.

Configuration 3

In the seismic isolation device according to configuration 1 or 2, thecomposite metal core has a rectangular shape or a slightly taperedrectangular shape in a vertical cross-section, and both the outer metaland the inner metal have one of a circular shape, an approximatelyquadrate shape, and an approximately polygonal shape having fewer anglesthen octagon in the horizontal cross-sectional. When the outer metal hasa circular shape in the plane view, two or more longitudinal ribsextending in the vertical direction are formed on the outer peripheralsurface of the outer metal. When the inner metal has a circular shape inthe plane view, two or more longitudinal engaging members are formed onthe inner peripheral surface of the outer metal and the outer peripheralsurface of the inner metal to be engaged with each other.

Configuration 4

In the seismic isolation devise according to any one of configurations 1to 3, the outer metal comprises tin or tin alloy and the inner metalcomprises lead or lead alloy. Both the outer metal and the inner metalhave one of a circular shape, an approximately quadrate shape, and anapproximately polygonal shape having fewer angles then octagon in thehorizontal cross-sectional view. A thickness t1 of the outer metal inthe cross-sectional plane view is set to satisfy an equation t1/dp≦0.35,the dp being a size of the composite metal core in the horizontalcross-sectional view.

Configuration 5

In the seismic isolation devise according to any one of configurations 1to 4, one or

two lid member, which is screw-cut, for fixing a core is incorporated ata plane center part of an upper end and/or a lower end of the compositemetal core. The lid member comprises copper or copper alloy.

Configuration 6

In a manufacturing method of the composite metal core of the seismicisolation device according to any one of configurations 1 to 5, when theouter metal has a melting point higher than the inner metal, thecomposite metal core is manufactured by injecting the inner metal, whichis in a molten state at a temperature lower than the melting point ofthe outer metal, into a hollow formed by an inner surface of the outermetal formed in a prescribed size and shape, or when the outer metal hasa melting point lower than the inner metal, the composite metal ismanufactured by injecting the outer metal, which is in a molten state ata temperature lower than the melting point of the inner metal, into ahollow formed between a metal mold having an internal shape equal to anouter surface of the outer metal, and the internal metal which is formedin advance and disposed inside the hollow.

Configuration 7

In the manufacturing method according to any one of configurations 1 to5, the composite metal core is manufactured as a metallic skin byimmersing the inner metal, which is formed in a prescribed size andshape in advance, into a container in which the outer metal is in amolten state, or the composite metal core is manufactured as a thin filmby thermal-splaying the outer metal, which is in a molten state, on atleast a side surface of the inner metal, which is formed in a prescribedsize and shape in advance.

Effect of the Present Invention

Effect 1

In the present invention, the horizontal shear resistance force can beset arbitrary. Specifically, since the metal core incorporated in thelaminated rubber bearing body is a hybrid core comprising two differentkinds of metal materials, the horizontal shear resistance force can beset arbitrary between the shear resistance force when the metal core isformed of one metal and the shear resistance force when the metal coreis formed of the other metal.

More specifically, the horizontal shear resistance force QC of acomposite metal core C in a predetermined cross-sectional area can bearbitrarily set to satisfy the following equation: QB≦QC<QA. The QA is ahorizontal shear resistance force in the predetermined cross-sectionalarea of a metal core A comprising the single outer metal. The QB is ahorizontal shear resistance force in the predetermined cross-sectionalarea of a metal core B comprising the single inner metal.

Note that the QC is approximately equal to the QB (QC≈QB) when the outermetal core A is formed as a metallic skin or a thin film made bythermal-splaying as described in the composition 7.

Effect 2

In the present invention, the rigidity (horizontal shear resistanceforce per unit area) of the metal core can be also set freely, likewisethe above first effect.

The average shear yield stress degree τ3 of the composite metal core perunit area is indicated with an equation τ3=τ1×RA1+τ2 (1−RA1). The τ1indicates the shear yield stress degree of the outer metal. The τ2indicates the shear yield stress degree of the inner metal. The RA1(=A1/A0) indicates the ration of the cross-sectional area of the outermetal A1 to the total cross-sectional area A0 of the composite metalcore.

With this configuration, the horizontal shear yield stress degree τ3 canbe arbitrary set to satisfy an equation τ2≦τ3<τ1, by changing the arearatio RA1.

Effect 3

A contribution of very small cross-sectional areas to a cross-sectionalsecondary moment I, which decides a bending rigidity of a metal core, isproportional to the square of the distance between a center of core andeach very small cross-sectional area. Therefore, the very smallcross-sectional area far from the center contributes the cross-sectionalsecondary moment I more than the very small cross-sectional area nearthe center.

Therefore, a relationship between an increase rate CEI (=EI3/EI2) (EI3:a bending rigidity of a composite metal core, where a material employedin the outer metal has a higher elastic modulus than a material employedin the inner metal, EI2: a bending rigidity of a metal core formed ofthe single inner metal core) and CGA (=GA3/GA2) (GA3: a shear rigidityof a composite metal core, where a material employed in the outer metalhas a higher elastic modulus than a material employed in the innermetal, GA2: a shear rigidity of a metal core formed of the single innermetal core) is indicated CEI>CGA, generally.

Accordingly, a composite metal core of the present invention has ahigher increase rate in the bending rigidity than the shear rigidity,and then a bending deformation is less likely to occur, when thecomposite metal core is subject to a horizontal force. In short, sincethe bending deformation is hard to occur, the composite metal core ofthe present invention becomes a shear deformation superior mode. Thissecures a stable shear deformability of the metal core, and the metalcore becomes to show a stable energy absorbing property.

Effect 4

In the present invention, since the composite metal core employs leadfor the inner metal and employs the other material such as tin insteadof lead for the outer metal, the inner metal comprising lead havingtoxicity to human body is covered by nontoxic outer metal. This helps toimprove the safety handling in manufacturing process, and to makeoperators' working environment safe and healthy.

In the present invention, when the outer metal is formed as thin film bythermal spraying or plating on the inner metal, the mechanic propertiesof the composite metal core becomes almost the same as the mechanicproperties of the inner metal (i.e. lead). Then, the composite metalcore of nontoxic in handling, while having almost the same mechanicalproperties as the inner metal, is materialized.

Effect 5

In the present invention, the weakness of the laminated rubber bearingbody incorporating tin is overcome.

A seismic isolation devices including a laminated rubber bearing bodyincorporating tin is successfully employed recently as a seismicisolation device incorporating a metal core other than lead metal core.However, the device has a weakness in thermal properties as pointed outherein above.

However, in the present invention having the outer metal comprising tinand the inner metal comprising lead, the heat generated in tin part canbe transferred to lead part having a large heat capacity and generatinga low heat. This avoids the temperature rise in the tin part andincreases the heat capacity of the whole the composite metal core. Leadhaving a high melting point compensates the thermal deterioration oftin. In this way, compared to the laminated rubber bearing bodyincorporating single tin, the vulnerability to generated heat of thewhole device is improved greatly. As the result, the weakness of thermalproperties of the tin metal core is overcome.

Effect 6

In the present invention, when the composite metal core has a circularplane shape, two or more longitudinal ribs are formed on the outerperipheral surface of the composite metal core (outer metal), and two ormore engaging members are formed on the inner peripheral surface of theouter metal and the outer peripheral surface of the inner metal to beengaged with each other. However, no longitudinal rib and engagingmember are required when the composite metal core has a polygonal shapesuch as a quadrate shape.

As a result, when the seismic isolation device is forcibly subject todeformation in two directions horizontally at a time, and especiallywhen the seismic isolation device is forcibly subject to rotationalexcitation so that the top surface is twisted against the bottomsurface, the metal core cannot rotate around a vertical axis inside thelaminated rubber bearing. Therefore, the device shows stable energyabsorption performance in a process of plastic deformation against anyexcitation mode including circular excitation.

Further, when a composite metal core has a quadrate plane shape (sidelength D), the cross-sectional area becomes 1.27 times (=4/π) largerthan a conventional metal core having a circular plane shape (diameterd) in a condition of (D=d). Therefore, the damping performance (energyabsorption performance) of the device is also improved.

Further, the present invention has an economic effect. One of theproblems of tin core is a cost. Since tin is extremely expensive, theprice of tin core becomes also extremely expensive. However, thecomposite metal core of the present invention employs lead for the innermetal and tin for the outer metal, and further the thickness of tin ofouter metal can be controlled appropriately. By this way, material costcan be reduced to an appropriate level, while overcoming the problems oftoxicity and improving the rigidity.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(1)-(2) show a basic structure of a conventional seismicisolation device incorporating a damper, wherein (1) is a verticalcross-sectional view showing that a core is disposed at a center of alaminated rubber bearing body, and wherein (2) is a horizontalcross-sectional view showing that the core having a circular shape isdisposed at a center part of the laminated rubber bearing body in theplane view.

FIGS. 2(1)-(2) are an explanatory diagram of a first embodiment of thepresent invention showing the whole basic structure of a seismicisolation device incorporating a composite metal core, wherein (1) is avertical cross-sectional view showing that the composite metal core isdisposed at a center part of a laminated rubber bearing body, andwherein (2) is a horizontal cross-sectional view showing that the corehaving a square shape is disposed at the center part of the laminatedrubber bearing body in the plane view.

FIGS. 3(1A)-(3B) are an explanatory diagram of a second embodiment(configuration 3) of the present invention, wherein (1A) is a horizontalcross-sectional view showing that four longitudinal ribs are formed onthe outer peripheral surface of the outer metal and four longitudinalengaging members are formed on the inner peripheral surface of the outermetal 31 and the outer peripheral surface of the inner metal when boththe outer metal and the inner metal have a circular shape, wherein (2A)is an elevational view of the composite metal core shown in (1A),wherein (3A) is a vertical cross-sectional view showing that thecomposite metal core shown in (1A) and (2A) incorporates a pair of lidmembers in the upper and lower ends, wherein (1B) is a horizontalcross-sectional view showing a composite metal core having anapproximately quadrate shape, wherein (2B) is an elevational view of thecomposite metal core shown in (1B), and wherein (3B) is a verticalcross-sectional view showing that the composite metal core shown in (1B)and (2B) incorporates a pair of lid members in the upper and lower ends.

FIGS. 4(1A)-(2B) are an explanatory diagram of a composite metal coremanufactured in configuration 7 according to a third embodiment of thepresent invention, wherein (1A) is a horizontal cross-sectional view ofa composite metal core having a circle plane shape, four longitudinalribs being formed on the outer peripheral surface of the outer metal,four longitudinal members being formed on the inner peripheral surfaceof the outer metal and the outer peripheral surface of the inner metalto be engaged with each other, the composite metal core being mainlycomprising the inner metal in the horizontal cross-sectional view, sincethe outer metal is a thin film by plating or thermal-spraying, wherein(2A) is an elevational view of the composite metal core shown in (1A),wherein (1B) is a horizontal cross-sectional view of a composite metalcore having an approximately quadrate plane shape, the composite metalcore being mainly comprising the inner metal in the horizontalcross-sectional view, since the outer metal is a thin film by plating orthermal-spraying, and wherein (2B) is an elevational view of thecomposite metal core shown in (1B).

FIG. 5 is an explanatory diagram of a composite metal core according toa forth embodiment of the present invention, wherein the change in theaverage shear yield stress intensity degree τ of the composite metalcore in accordance with the ratio of the thickness of the outer metal tothe diameter of the composite metal core having a circular or quadrateplane shape is illustrated, when the composite metal core has a planecircular shape or a square shape, and when the outer metal comprises tinand the inner metal comprises lead.

FIG. 6 is an explanatory diagram of a fifth embodiment of the presentinvention, wherein the change in the horizontal shear resistance forceQd of the composite metal core, in accordance with the plane size(diameter) of the composite metal core and the thickness of the outermetal is illustrated, when the composite metal core has a plane circularshape, and when the outer metal comprises tin and the inner metalcomprises lead.

FIG. 7 is an explanatory diagram of a sixth embodiment of the presentinvention, wherein the change in the horizontal shear resistance forceQd of the composite metal core in accordance with the plane size (sidelength) of the composite metal core and the thickness of the outer metalis illustrated, when the composite metal core has a quadrate planeshape, and when the outer metal comprises tin and the inner metalcomprises lead.

FIG. 8 is an explanatory diagram of a seventh embodiment of the presentinvention, wherein the rising rate of bending rigidity EI and shearrigidity GA of a composite metal core in accordance with an area ratio(A1/A0) of an area (A1) of the outer metal to an area (A0) of the wholecomposite metal core is illustrated, the outer metal comprising tin, theinner metal comprising lead.

FIG. 9 is an explanatory diagram of an eighth embodiment of the presentinvention, wherein the rising rates of bending rigidity EI and shearrigidity GA of a composite metal core in accordance with a ratio(2t1/dp) of the thickness of the outer metal to a diameter of thecomposite metal core, wherein the outer metal comprises tin and theinner metal comprises lead, and wherein the rising rate of the curvewill be common when the composite metal core has either circular planeshape or quadrate plane shape, as long as the outer metal and the innermetal have the same plane shape and the thickness t1 of the outer metalis even.

FIGS. 10(1)-(3) are an explanatory diagram of an effect according to asixth effect of the present invention, wherein (1) is a verticalcross-sectional view showing a state where a laminated rubber bearingbody incorporating a core in the center is subject to a forciblydeformation in the horizontal direction (direction 5), wherein (2) is anexplanation diagram showing a rotation in direction 8 of a core in aconventional seismic isolation device, when the laminated rubber bearingis forcibly deformed to rotate in direction 8 by deforming in direction5 and then indirection 6, and wherein (3) is an explanation diagramshowing that a core having quadrate plane shape (or of circular shapehaving longitudinal ribs) of the present invention is unable to rotatearound a vertical axis, even when the same deformation as above (2) isforced to the laminated rubber bearing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present invention are explained based on thedrawings. The same number will be used to indicate the same part in therespective embodiments.

Embodiment 1

FIG. 2 shows a first embodiment of the present invention with respect tothe configurations 1 and 2. FIG. 2 (1) is a vertical cross-sectionalview, and FIG. 2(2) is a horizontal cross-sectional view.

A seismic isolation device according to the first embodiment is a damperbuilt-in type of laminated rubber bearing seismic isolation device. Theseismic isolation devise includes a laminated rubber bearing body 1 andat least one plastic metal core 30. The laminated rubber bearing body 1is formed by alternately laminating a plurality of elastic layers(elastic materials) 11 and a plurality of inner steel plates (rigidmaterials) 2 in the vertical direction, each elastic layer 11 and eachinner steel plate 2 having a thin plate shape. The plastic metal core 30is plastically deformable to absorb energy and is disposed inside thelaminated rubber bearing body 1. Thus, the plastic metal core 30 servesas a damper mechanism.

The plastic metal core 30 includes two kinds of metals (an inner metal32 and an outer metal 31) having different plastic deformability inyield rigidity and elastic modulus with each other. These metals arearranged in concentric in a horizontal cross-sectional view. In otherwords, the outer metal 31 concentrically surrounds the inner metal 32 inthe horizontal cross-sectional view.

The outer metal 31 and the inner metal 32 are disposed in closeadherence with each other and integrated. The integrated outer metal 31and inner metal 32 forms a composite metal core 30. The outer metal 31has an elastic modulus and an yield intensity greater than the innermetal 32. The composite metal core 30 has an approximately square shapein the plane view, as shown in the FIG. 2 (2).

By composing the outer metal 31 of the material with the verticalelastic modulus and the yield intensity greater than the inner metal 32,it becomes possible to greatly raise an increase rate of a bendingrigidity of the composite metal core 30 rather than an increase rate ofa shear rigidity of the composite metal core 30 (see FIG. 8), comparedto the plastic metal core comprising the single inner metal 32 in thesame plane sectional size. As a result, the bending deformability of theplastic metal core 30 becomes smaller, and the shear deformabilitybecomes greater than bending deformability in the plastic metal core 30.Thus, the shear plastic deformation is stabilized and a stable energyabsorption performance in the process of plastic deformation can besecured.

Thick steel plates 25 are disposed near the upper and lower ends of thecomposite metal core 30. Flanged steel plates 4 are disposed outside ofthe thick steel plates 25 in the upper-lower direction.

Any one of Combinations 1 to 4 (Combination 1: tin for the outer metal31 and lead for the inner metal 32, Combination 2: aluminum for theouter metal 31 and lead or tin for the inner metal 32, Combination 3:zinc for the outer metal 31 and any one of lead, tin and aluminum forthe inner metal 32, Combination 4: copper for the outer metal 31 and anyone of lead, tin, aluminum and zinc for the inner metal 32) are employedas a combination of a material composing the outer metal 31 and amaterial composing the inner metal 32.

Combination 1, (i.e. tin for the outer metal 31 and lead for the innermetal 32) is a representative example, although any combination of theabove can be employed. Note that each material described above caninclude alloy of them.

With this construction, a horizontal shear resistance force QC of acomposite metal core C in a predetermined cross-sectional area can bearbitrarily set to satisfy an equation: QB≦QC<QA, the QA being ahorizontal shear resistance force in the predetermined cross-sectionalarea of a metal core A comprising the single outer metal 31, the QBbeing a horizontal shear resistance force in the predeterminedcross-sectional area of a metal core B comprising the single inner metal32.

Embodiment 2

FIG. 3 shows an embodiment of the configuration 3 of the presentinvention. FIG. 3(1A) to (3A) illustrates the composite metal core 30having a circular plane shape. FIG. 3 (1A) is a horizontalcross-sectional view of the composite metal core 30. FIG. 3 (2A) is anelevational view of the composite metal core 30, showing longitudinalribs 33 in the peripheral side. FIG. 3 (3A) is a verticalcross-sectional view of the composite metal core 30.

The composite metal core 30 has a rectangular shape or a slightlytapered rectangular shape in the vertical cross-section. Both the outermetal 31 and the inner metal 32 have one of a circular shape, anapproximately quadrate shape, or an approximately regular polygonalshape having angles fewer than or equal to octagon in the horizontalcross-section (in the plane view).

As shown in FIG. 3(1A), when both the outer metal 31 and the inner metal32 have a circular shape in the plane view, four (two or more)longitudinal ribs 33 extending in the vertical direction are formed onthe outer peripheral surface of the outer metal 31. Further, four (twoor more) longitudinal engaging members 34 (concavities and convexitiesextending in the vertical direction) are formed on the inner peripheralsurface of the outer metal 31 and the outer peripheral surface of theinner metal 32 to be engaged with each other.

Further, as shown in FIG. 3 (3A), a pair of lid member 36, which isscrew-cut and used in a suspension operation in a manufacturing of thelaminated rubber bearing body 1, is incorporated at a plane center partof the upper and lower ends of the composite metal core 30.

The pair of lid member 36 has a “protrusion preventing function” forpreventing the materials composing the composite metal core 30 fromprotruding upward and downward due to an earthquake vibration.

Further, the pair of lid member 36 has a “deformation correctingfunction.” When the pair of lid member 36 comprises copper or copperalloy, it becomes possible to apply current to the composite metal core30 thorough the pair of lid member 36. By applying current to thecomposite metal core 30, it is possible to raise the temperature of thecomposite metal core 30. When the temperature of the composite metalcore 30 is raised, the composite metal core 30 becomes soft. Therefore,even if the composite metal core 30 is deformed by the earthquake, thedeformation of the composite metal core 30 can be easily corrected byapplying current.

Furthermore, the pair of lid member 36 has a “metal structureregenerating function.” By heating and thereafter cooling the compositemetal core 30, it becomes possible to eliminate the plastic distortionof the composite metal core 30, and then restore the structure of thecomposite metal core 30 (prompt the composite metal core 30 to bere-crystallized).

FIG. 3 (1B) to (3B) shows the composite metal core 30 having anapproximately quadrate plane shape. FIG. 3 (1B) is a horizontalcross-sectional view of the composite metal core 30. FIG. 3(2B) is anelevational view of the composite metal core 30. FIG. 3(3B) is avertical cross-sectional view of the composite metal core 30.

When the composite metal core 30 has a quadrate or polygonal planeshape, the peripheral side surface of the composite metal core 30 (outermetal 31) is engaged with the inner steel plates 2, the thick steelplates 2, and the flanged steel plates 4 (depending on the shape).Therefore, in such case, the longitudinal ribs 33 are unnecessary, sincethe rotational shift around a vertical axis does not occur in thecomposite metal core 30. Further, in such case, the outer metal 31 andthe inner metal 32 are also engaged with one another. Therefore, in suchcase, the four longitudinal engaging members 34 are also unnecessary,since the rotational shift around the vertical axis does not occur.

In FIG. 3 (3B), the function of the pair of lid member 36 provided onthe upper and the lower ends of the composite metal core 30 is asexplained in FIG. 3(3A).

As shown in FIGS. 3 (3A) and (3B), horizontal engaging members 35(concavities and convexities) are formed on the inner peripheral surfaceof the outer metal 31 and the outer peripheral surface of the innermetal 32 to be engaged with each other. These horizontal engagingmembers 35 are stoppers for preventing the shift in vertical directionfrom occurring between the outer metal 31 and the inner metal 32, whenthe composite metal core 30 is forced to deform in the horizontaldirection. Owing to the horizontal engaging members 35, the outer metal31 and the inner metal 32, which comprises two kinds of metals, isdistorted in the horizontal direction as a unit. Therefore, the plasticdeformation of the outer metal 31 and the inner metal 32 occurs evenly.As the result, a stable energy absorption performance is conducted.

In the configuration 6, a method for manufacturing the composite metalcore 30 by utilizing the difference in the melting point between theouter metal 31 and the inner metal 32 is described.

When the outer metal 31 has a melting point higher than the inner metal32, the composite metal core 30 is manufactured by injecting the innermetal 32, which is in a molten state at a temperature lower than themelting point of the outer metal 31, into a hollow formed by the innersurface of the outer metal 31 formed in a prescribed size and shape.

On the other hand, when the outer metal 31 has a melting point lowerthan the inner metal 32, the composite metal 30 is manufactured byinjecting the outer metal 31, which is in a molten state at atemperature lower than the melting point of the inner metal 32, into ahollow formed between a metal mold having an internal shape equal to theouter surface of the outer metal 31, and the internal metal 32 which isformed in advance and disposed inside the hollow.

Embodiment 3

FIG. 4 shows an embodiment of the configuration 7 of the presentinvention. FIGS. 4 (1A) and (2A) shows the composite metal core 30having a circular plan shape. FIGS. 4 (1B) and (2B) shows the compositemetal core 30 having an approximately quadrate plane shape. FIGS. 4 (1A)and (1B) are horizontal cross-sectional view of the composite metal core30. FIGS. 4 (2A) and (2B) are elevational view of the composite metalcore 30.

In this embodiment, the composite metal core 30 is manufactured as ametallic skin by immersing the inner metal 32, which is formed inprescribed size and shape in advance, into a container in which theouter metal 31 is in a molten state. Further, the composite metal core30 is also manufactured as a thin film by thermal-splaying the outermetal 31, which is in a molten state, on at least the side surface ofthe inner metal 32, which is formed in prescribed size and shape inadvance.

As the outer metal 31 is formed as the metallic skin or the thin filmwith the above manufacturing methods, the outer metal 31 is illustratedas an outline 311 in the figure, and the plan area is mainly accountedfor the inner metal 32.

With this construction, by covering/coating the inner metal 32comprising lead with tin, aluminum or other non-toxic metal composingthe outer metal 31 (311), an environment/health-friendly seismicisolation device, while having the mechanical property of lead, ismaterialized. Through this embodiment, the problem of toxicity of thelead-cored laminated rubber bearing is overcome. In this embodiment,since the outer metal 31 is formed as the thin film, the resistanceforce QA of the outer metal 31 becomes very low, and the resistanceforce QC of the composite metal core C becomes closer to the resistanceforce QB of the inner metal B (QC≈QB).

Embodiment 4

FIG. 5 shows a composite effect of two kinds of metals described in theconfigurations 1 and 2 of the present invention. Specifically, FIG. 5shows changes in an average shear stress degree τ of the composite metalcore 30, which is a combination of the outer metal 31 comprising tin andthe inner metal 32 comprising lead, in accordance with the ratio 2t1/dpof the thickness t1 of the outer metal 31 to the diameter dp of thecomposite metal core 30.

In FIG. 5, a horizontal shear resistance force (average shear stressdegree) τ at 2t1/dp=0 is equal to the shear yield stress degree τ=8(N/mm²) of the inner metal 32 comprising lead. When the outer metal 31is formed as a thin film as described in the third embodiment, theaverage shear stress degree τ almost indicates this value.

As shown in FIG. 5, the horizontal shear resistance force T of thecomposite metal core 30 is increased in accordance with the increase ofthe thickness of the outer metal 31. At 2t1/dp=1, the horizontal shearresistance force (average shear stress degree) τ of the composite metalcore 30 becomes equal to the shear yield stress degree τ≈15 (N/mm²) ofthe outer metal 31 comprising tin. In this state, the composite metalcore 30 is formed with the single outer metal 31.

As is shown in the FIG. 5, in the present invention, it becomes possibleto set the average shear stress intensity degree T to an arbitrary valuebetween the horizontal shear resistance forces of the two metals, byselecting the combination way of two kinds of metals.

Note that this graph can be also applied when the composite metal core30 has either one of a circle or quadrate plane shape, and further whenthe composite metal core 30 has a polygonal plane shape, as long as theouter metal 31 and the inner metal 32 are concentric and the thicknesst1 of the outer metal 31 is even.

Embodiment 5

FIG. 6 illustrates the relationship between a plane size (plug diameterdp) of the composite metal core (plug) 30 and the horizontal shearresistance force Qd, when the outer metal 31 comprises tin and the innermetal 32 comprises lead, and when the composite metal core 30 has acircular plane shape.

The plug diameter dp is set in the range of 100 mm to 300 mm. Amongseveral curves in FIG. 6, the bottom curve represents the horizontalshear resistance force Qd when the whole composite metal core 30comprises single lead (the inner metal 32), and the top curve representsthe horizontal shear resistance force Qd when the composite metal core30 comprises single tin (the outer metal 31). It is found that thehorizontal shear resistance force Qd can be efficiently increased byonly increasing the thickness t1 of the outer metal 31. For example, byincreasing the thickness t1 10 mm up to 50 mm when the plug diameter dpis 300 mm, the horizontal shear resistance force Qd is efficientlyincreased.

Embodiment 6

FIG. 7 illustrates the relationship between a side length dp of thecomposite metal core 30 and the horizontal shear resistance force Qdwhen the outer metal 31 comprises tin and the inner metal 32 compriseslead, and when the composite metal core 30 has a quadrate plane shape.

The side length dp is set in the range between 100 mm to 300 mm. Amongseveral curves, the bottom curve represents the horizontal shearresistance force Qd when the whole composite metal core 30 comprisessingle lead (the inner metal 32), and the top curve represents thehorizontal shear resistance force Qd when the whole composite metal core30 comprises single tin (the outer metal 31). Same as FIG. 6, by onlyincreasing the thickness t1 of the outer metal 31, the horizontal shearresistance force Qd can be efficiently increased. For example, byincreasing the thickness t1 10 mm up to 50 mm when the side length dp is300 mm, the horizontal shear resistance force Qd is efficientlyincreased.

Further, by employing the quadrate shape instead of the circle shape,the horizontal shear resistance force Qd can be more efficientlyincreased.

Embodiment 7

FIG. 8 shows a rising rate EI/EIpb of a bending rigidity EL and a shearrigidity GA in accordance with the composition rate of the metals in thecomposite metal core 30. The metal comprises a combination of tin (theouter metal 31) and lead (the inner metal 32), similar to the previousexample. A0 indicates an area of the whole composite metal core 30, andA1 indicates an area of the outer metal 31. Further, it is assumed thatthe composite metal core 30 has a circular plane shape and has a plugdiameter dp between 100 mm to 300 mm while this graph can be applied toany size of composite metal core 30.

Among several straight lines, the bottom straight line (A1/A0=0), whichis set to a reference value (=1), represents the rising rate EI/EIpbwhen the whole composite metal core 30 comprises single lead, and thetop straight line (A1/A0=1) represents the rising rate EI/EIpb when thewhole composite metal core 30 comprises single tin. The rising rateEI/EIpb of the bending rigidity EI corresponds to the ratio of thelongitudinal elastic modulus of tin and lead. The rising rate EI/EIpb ofthe shear rigidity GA corresponds to the ratio of the shear elasticitymodulus of tin and lead. The middle lines shows the ratio A1/A0 of thearea A1 of the outer metal 31 (tin) to the whole cross-sectional area A0of the composite metal core 30.

It is clear that the rising rate EI/EIpb of the bending rigidity EL ishigher than the rising rate GA/GAbp of the shear rigidity GA whencompared in the same area ratio A1/A0. This is one of the importantpoints of the present invention.

Embodiment 8

FIG. 9 shows rising rates of the bending rigidity EI and the shearrigidity GA of the composite metal core 30. In FIG. 9, the horizontalaxis indicates a ratio 2t1/dp of a thickness t1 of the outer metal 31 toa diameter dp of the composite metal core 30 having a circle shape. Theouter metal 31 comprises tin and the inner metal 32 comprises lead,similar to the previous example. The rising rates of the bendingrigidity EI and the shear rigidity GA when the whole cross-section ofthe composite metal core 30 comprises lead is set as a referencevalue=1.

As shown in FIG. 9, the rising rate of the bending rigidity EI exceedsthe rising rate of the shear rigidity GA in the range of 2t1/dp=0 to0.7, and the rising rate of share rigidity GA exceeds that of bendingrigidity EI in the range not less than 2t1/dp=0.7.

Accordingly, by setting the thickness t1 of the outer metal 31 in therange of t1/dp=0 to 0.35 when the outer metal 31 comprises tin and theinner metal 32 comprises lead, the shear deformation tends to occur morethan the rigidity deformation in the composite metal core 30 of thepresent invention. Therefore, a stable energy absorption performance isexpected.

This graph is also applied when the composite metal core 30 has eithercircular plane shape or quadrate plane shape, and when the compositemetal core 30 has a polygonal plane shape as long as the outer metal 31and the inner metal 32 are concentric, the thickness of the outer metal31 is even, and the plane shape of the outer metal 31 is symmetric tothe central axis (a neutral axis) of the outer metal 31 in thecross-section.

Embodiment 9

Considering the FIGS. 6, 7 and 9 at the same time, the present inventionhas excellent effects. Specifically, when the outer metal 31 comprisestin and the inner metal core 32 comprises lead, by only setting thethickness t1 of the outer metal 31 to 10 to 20 mm (setting 2t1/dp≈0.1 to0.2 for a standard core size of dp=200 mm) at best, the horizontal shearresistance force Qd of the composite metal core 30 can be drasticallyincreased and the bending rigidity EI of the composite metal core 30 canbe also drastically increased. As the result, the composite metal core30 enters a shear deformation superior mode in which the sheardeformation exceeds the rigidity deformation, thereby conducting astable energy absorption performance.

If the composite metal core 30 comprising single tin is repeatedlylargely deformed by a large earthquake, the horizontal shear resistanceforce Qd is drastically declined. As the result, in a possible worstcase, the composite metal core 30 may be melted due to a temperaturerise caused the repeated large deformations.

However, in the shear deformation superior mode described above, a largeheat capacity is secured in the whole composite metal core 30 due tolead composing the inner metal 32 (lead account for 90 to 81% of theplane area of the composite metal core 30). Therefore, heat generated atthe outer metal 31 comprising tin is promptly transmitted to the innermetal 32 comprising lead, thereby inhibiting the temperature rise in thewhole composite metal core 30. Thus, in the composite metal core 30 ofthe present invention, the risk of the decline of the horizontal shearresistance force Qd or the risk of melting itself, caused by thetemperature rise, is drastically improved and overcome.

FIG. 10 shows an embodiment of one of the effects of the rubber seismicisolation device incorporating the composite metal core 30 of thepresent invention.

FIG. 10(1) is a vertical cross-sectional view showing a state where thelaminated rubber bearing body 1 is subject to a horizontal sheardeformation force Qd in a direction of arrow 5 (deformation 1). Inaccordance with a horizontal deformation of the laminated rubber bearingbody 1, a metal core 3 deforms as illustrated in the figure.Specifically, the top surface 38 of the metal core 3 is shifted the sameamount as the horizontal deformation of the laminated rubber bearingbody 1, from the original position right over the bottom surface 37 ofthe metal core 3.

If, after this movement, the top surface 38 of the laminated rubberbearing body 1 is shifted in a direction 6 (shown in FIG. 10 (2))horizontally orthogonal to the direction 5, a force acting in thedirection 6 is changed to a moment (twisting force) for rotating themetal core 3 around an own vertical axis as shown in a direction ofarrow 8. If the metal core 3 has just a cylindrical shape, the metalcore 3 rotates separately from the laminated rubber bearing body 1inside the laminated rubber bearing body 1. Then, the plastic sheardeformation does not occur in the core 30. Then, the energy absorptionperformance of the core 30 is not conducted.

However, in the present invention, the composite metal core 30 isdesigned to have a polygonal (quadrate or the like) plane shape.Otherwise, when the composite metal core 30 is designed to have acircular plane shape, two or more longitudinal ribs 33 are formed on theouter peripheral surface of the composite metal core 30 (outer metal 31)as shown in FIGS. 3 and 4.

In this way, even when the seismic isolation device is forced to deformin horizontal two directions at a time, especially when the seismicisolation device receives an excitation for the top surface 38 tohorizontally rotate in the direction of arrow 7 against the position ofthe bottom surface 37, the composite metal core 30 is prevented fromrotating around the own vertical axis inside the laminated rubberbearing body 1. Thus, the composite metal core 30 attains an excellentperformance for absorbing energy by the plastic deformation, even whenthe composite metal core 30 is subject to any excitation includingcircular excitation.

As described above, in the laminated rubber bearing body 1 of thepresent invention, it becomes possible to control the horizontal shearresistance force Qd of the composite metal core 30 at an appropriatelylevel, although it is not possible when a conventional metal corecomprises a single metal. Therefore, a stable energy absorptionperformance is provided. As the result, a performance and reliability ofa conventional type of damper built-in laminated rubber bearing body isgreatly improved.

Since the Great East Japan Earthquake (M9.0), which hit Japan in 2011, acatastrophic earthquake of the level of M 9.0 has been recognized as arealistic one to occur. Therefore, the effect of the seismic isolationdevise of the present invention is expected to play an effective role,assuming that a long-period and continuous severe earthquake vibration,or a severe input earthquake vibration in horizontal two directionsoccurs.

1-15. (canceled)
 16. A seismic isolation device comprising: a laminatedrubber bearing body formed by alternately laminating a plurality ofelastic materials and a plurality of rigid materials in a verticaldirection, each elastic material and each rigid material having a plateshape; and a metal core disposed inside the laminated rubber bearingbody in a vertical direction and plastically deformable to absorbenergy, wherein the metal core has an approximately quadrate shape, oran approximately polygonal shape having fewer angles than octagon in thehorizontal cross-sectional view.
 17. The seismic isolation deviceaccording to claim 16, further comprising the laminated rubber bearingbody and a composite metal core disposed inside the laminated rubberbearing body in a vertical direction and plastically deformable toabsorb energy, wherein the composite metal core includes an inner metaland an outer metal, the outer metal concentrically surrounding the innermetal in a horizontal cross-sectional view, the inner metal and theouter metal being disposed in close adherence with each other, the outermetal having an elastic modulus and a yield rigidity greater than theinner metal so that a shear deformability of the composite metal corebecomes greater than a bending deformability of the composite metalcore, and wherein a horizontal shear resistance force QC of thecomposite metal core in a predetermined cross-sectional area is set tosatisfy an equation: QB≦QC<QA, the QA being a horizontal shearresistance force in the predetermined cross-sectional area of a metalcore A comprising the single outer metal, and the QB being a horizontalshear resistance force in the predetermined cross-sectional area of ametal core B comprising the single inner metal.
 18. The seismicisolation device according to claim 16, wherein the inner metalcomprises lead or lead alloy and the outer metal comprises any one oftin, tin alloy, aluminum, aluminum alloy, zinc, zinc alloy, copper andcopper alloy.
 19. The seismic isolation device according to claim 17,wherein the inner metal comprises lead or lead alloy and the outer metalcomprises any one of tin, tin alloy, aluminum, aluminum alloy, zinc,zinc alloy, copper and copper alloy.
 20. The seismic isolation deviceaccording to claim 18, wherein a thickness t1 of the outer metal in thecross-sectional plane view is set to satisfy an equation t1/dp≦0.35, thedp being a size of the composite metal core in the horizontalcross-sectional view.
 21. The seismic isolation device according toclaim 19, wherein a thickness t1 of the outer metal in thecross-sectional plane view is set to satisfy an equation t1/dp≦0.35, thedp being a size of the composite metal core in the horizontalcross-sectional view.
 22. The seismic isolation device according toclaim 16, wherein the inner metal comprises tin or tin alloy and theouter metal comprises any one of aluminum, aluminum alloy, zinc, zincalloy, copper and copper alloy.
 23. The seismic isolation deviceaccording to claim 17, wherein the inner metal comprises tin or tinalloy and the outer metal comprises any one of aluminum, aluminum alloy,zinc, zinc alloy, copper and copper alloy.
 24. The seismic isolationdevice according to claim 22, wherein a thickness t1 of the outer metalin the cross-sectional plane view is set to satisfy an equationt1/dp≦0.35, the dp being a size of the composite metal core in thehorizontal cross-sectional view.
 25. The seismic isolation deviceaccording to claim 23, wherein a thickness t1 of the outer metal in thecross-sectional plane view is set to satisfy an equation t1/dp≦0.35, thedp being a size of the composite metal core in the horizontalcross-sectional view.
 26. The seismic isolation device according toclaim 16, wherein the inner metal comprises aluminum or aluminum alloyand the outer metal comprises any one of zinc, zinc alloy, copper andcopper alloy.
 27. The seismic isolation device according to claim 17,wherein the inner metal comprises aluminum or aluminum alloy and theouter metal comprises any one of zinc, zinc alloy, copper and copperalloy.
 28. The seismic isolation device according to claim 26, wherein athickness t1 of the outer metal in the cross-sectional plane view is setto satisfy an equation t1/dp≦0.35, the dp being a size of the compositemetal core in the horizontal cross-sectional view.
 29. The seismicisolation device according to claim 27, wherein a thickness t1 of theouter metal in the cross-sectional plane view is set to satisfy anequation t1/dp≦0.35, the dp being a size of the composite metal core inthe horizontal cross-sectional view.
 30. The seismic isolation deviceaccording to claim 16, wherein the inner metal comprises zinc or zincalloy and the outer metal comprises copper or copper alloy.
 31. Theseismic isolation device according to claim 17, wherein the inner metalcomprises zinc or zinc alloy and the outer metal comprises copper orcopper alloy.
 32. The seismic isolation device according to claim 30,wherein a thickness t1 of the outer metal in the cross-sectional planeview is set to satisfy an equation t1/dp≦0.35, the dp being a size ofthe composite metal core in the horizontal cross-sectional view.
 33. Theseismic isolation device according to claim 32, wherein a thickness t1of the outer metal in the cross-sectional plane view is set to satisfyan equation t1/dp≦0.35, the dp being a size of the composite metal corein the horizontal cross-sectional view.
 34. The seismic isolation deviseaccording to claim 16, wherein one or two lid member, which isscrew-cut, for fixing a core is incorporated at a plane center part ofan upper end and/or a lower end of the composite metal core, and whereinthe lid member comprise copper or copper alloy.